The present invention relates to new and useful improvements in rolling bearings particularly for wheel bearing assemblies consisting of an inner ring having at least one radially outwardly directed flange for mounting the rim of the wheel, an outer ring and a plurality of rolling elements in the annular space between the rings and a cap secured to the inner ring having a radial section extending between the outer ring and the fastening flange and a seal ring secured to the outer ring which slides on the cap.
This general type of bearing assembly is not new per se as exemplified by the bearing arrangement shown in the German Utility Pat. No. 7,434,724. In this roller bearing, the radial section of the cap fits against the fastening flange of the inner ring and therefore covers the axially extending openings in the flange for the bolts mounting the wheel. A disadvantage, however, of this assembly, is that the seal ring which slides on the radial section of the cap, which is typically provided with an elastic sealing lip of a temperature sensitive material, for example, plastic, must endure relatively high operating temperatures when heat sources are present at the inner ring. In some cases this causes undue heating of the seal. For example, severe heating occurs when the roller bearing is filled with an excessive amount of lubricant or the inner ring tends to build excessive heat as a result of connected friction couplings or friction brakes where the inner ring dissipates the friction heat generated. A relatively high temperature can especially occur at the inner ring of the roller bearing which is connected to a disc brake and in these instances, the radial section of the cap may be heated to such an extent that the seal ring slides on this section and rises to such elevated temperatures to cause premature failure as a result of the sliding wear.
With the foregoing in mind, an object of the present invention is to provide improved roller bearing construction of the above mentioned type which eliminates overheating of the seal ring at its sliding location on the cap even when high temperatures are generated on the inner ring. This is achieved in accordance with the present invention by providing at least one space between the radial section of the cap and the fastening flange which space is filled at least in part with means for inhibiting the heat transfer from the inner ring to the cap. The filler means may simply comprise air which is circulated through the space or filling the space with a material having low heat conductivity. In accordance with the present invention therefore, the heat transfer between the radial section of the cap and the axially opposing fastening flange is inhibited. Thus, the radial section and the immediately adjacent sections of the cap are at a low operating temperature even when the inner ring is subjected to high loads. The arrangement therefore, eliminates the danger inherent in prior assemblies; that is, excessive heating of the seal ring which slides and rubs on the cap at its sliding location and failure of the seal ring after a short running time as a result of wear and/or thermal decomposition which may be exhibited, for example, as embrittlement of the plastic sealing lip.
Heat conduction from the fastening flange to the cap may be inhibited by using a gaseous, a liquid, or a solid material with a low heat conductivity. For example, asbestos, rubber or plastic may be used as a solid material. Gaseous mediums are also suitable however, and in this instance, the bearing assembly is a rather simplified construction and is economical to produce.
In accordance with another feature of the present invention, at least one air port is provided in the inner ring and/or the cap communicating with the space between the cap and flange and the outside environment. This arrangement provides a good convective exchange of the heated air in the space with the cool air of the environment. Furthermore, in a wheel bearing assembly where the wheel rim is fastened to the flange of the inner ring and the inner ring rotates, the air present in the space is conveyed radially outwardly through the air ports or openings formed between the radial section of the cap and the fastening flange by a centrifugal effect. Cooling air of the ball bearing environment is drawn through the air openings in the inner ring or in the cap into the spaces simultaneously.
In accordance with another feature of the present invention, means is provided for limiting the temperature rise of the cap notwithstanding how high the inner ring temperature attains. This is achieved by mounting a material having a relatively low melting temperature, for example, plastic or a low melting metal in the space between the cap and fastening flange. By this arrangement, when the inner ring is heated up for a short period of time, the heat energy of the fastening flange is consumed by the melting energy of the material in the space. For example, assuming the material has a melting temperature of 140.degree. C., then the cap and the seal ring sliding on the cap can only be heated to 140.degree. C. by reason of the protective material. As a result, the seal ring of the bearing has a high operating reliability and a long useful life. It is noted that instead of utilizing a plastic or low melting metal in the space, liquids such as oil which change their aggregate state from the liquid to the gaseous state when the highest permissable temperature is attained can also be utilized.
The specific configuration of the cap includes a radially extending center section and at least one axially extending centering extension. A cap of this configuration can be shaped rather easily and economically from strip material, for example, sheet metal by a non-cutting stamping and/or deep drawing operation. A cap of this configuration is easy to mount on the inner ring in order to support the cap in place.
In accordance with one embodiment of the invention, means such as asbestos having a low heat conductivity and good sealing properties is inserted in at least the space formed between the centering section of the cap and the inner ring. By this arrangement, heat conduction from the inner ring to the centering extension of the cap is inhibited. Furthermore, lubricant for the bearing is at the same time prevented from penetrating into the space between the flange and the cap and from there increasing the heat transfer from the inner ring to the cap as a result of its own heat conductivity and/or convection. Penetration of the lubricant would result in unfavorably high running temperatures of the cap and the seal ring sliding on the cap. The asbestos liner also serves the additional function by reason of its sealing properties of eliminating lubricant losses as a result of migration of the lubricant into the spaces.